Synthesis and characterization of high nitrile content polyimides as dielectric films for electrical energy storage |
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Authors: | David H Wang Brian A Kurish Imre Treufeld Lei Zhu Loon‐Seng Tan |
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Institution: | 1. Materials and Manufacturing Directorate, Soft Matter Materials Branch (AFRL/RXAS), Air Force Research Laboratory, Wright‐Patterson Air Force Base, Ohio;2. UES, Inc. 4401 Dayton‐Xenia Road Dayton, Ohio;3. Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio |
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Abstract: | Three new isomeric diamines containing three, oxy‐linked benzonitriles (3BCN), one of which is asymmetric (meta, para, or m, p), are synthesized in a 3‐step sequence. Polycondensation of these diamines and four common dianhydrides (6FDA, OPDA, BTDA, and PMDA) in N,N‐dimethylacetamide via poly(amic acid) precursors and thermal curing at temperatures up to 300 °C lead to three series of tough, creasable polyimide (PI) films (tensile moduli = 1.63 ? 2.86 GPa). Among these PIs, two PMDA‐based PIs possess relatively high crystallinity and two OPDA‐based PIs, low crystallinity, whereas all 6FDA‐ and BTDA‐based PIs, and m,m‐3BCN‐OPDA‐PI are amorphous, readily soluble in common polar aprotic solvents. Thermally stable and having high Tg (216 ? 341 °C), these PIs lose 5% weight around 493–503 °C in air and 463–492 °C in nitrogen. Dielectric properties have been evaluated by broadband dielectric spectroscopy (BDS) and electric displacement‐electric‐field (D‐E) loop measurements. D‐E loop results show an increase in high temperature permittivity (at 190 °C/1 kHz) from 2.9 (for parent PI CP2 with no nitrile group) to as high as 4.9 for these PIs, while keeping their dielectric loss relatively low. Thus, an increase in dipole moment density by the presence of three neighboring CN per repeat unit can increase the overall permittivity, which could be further enhanced by sub‐Tg mobility of para‐phenylene linkages (BDS results). Published 2014. J. Polym. Sci., Part A: Polym. Chem. 2014 J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 422–436 |
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Keywords: | benzonitrile diamine synthesis dielectric properties differential scanning calorimetry (DSC) FT‐IR monomers NMR polyimides synthesis sub‐Tg transitions thermogravimetric analysis (TGA) WAXD |
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